The small intestine transfers large volumes of fluid into and out of the lumen on a daily basis to facilitate digestion and absorption of nutrients, driven by active transport of ions and other electrolytes.
8.
The motor patterns of the small intestine vary depending on whether a meal has been ingested. Immediately after a meal, motility is directed to retaining the meal in the small intestine, mixing it with digestive juices, and providing sufficient time for absorption of nutrients. During fasting, a “housekeeper” complex of intense contractions (the migrating motor complex) sweeps periodically along the length of the stomach and small intestine to clear them of undigested residues.
Abumrad NA, Davidson NO. Role of the gut in lipid homeostasis. Physiol Rev. 2012;92:1061-1085.
Argent BE, et al. Cell physiology of the pancreatic ducts. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Barrett KE, Keely SJ. Electrolyte secretion and absorption in the small intestine and colon. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
Bharucha AE, Hasler WL. Motility of the small intestine and colon. In: Podolsky DK, et al., eds. Yamada’s Textbook of Gastroenterology. 6th ed. Hoboken, NJ: Wiley Blackwell; 2015.
Ganapathy V. Protein digestion and absorption. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Liddle RA. Regulation of pancreatic secretion. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Wright EM, Sala-Rabanal M, Loo DDF, Hirayama BA. Sugar absorption. In: Johnson LR, ed. Physiology of the GI Tract. 5th ed. Waltham, MA: Academic Press; 2012.
Upon completion of this chapter the student should be able to answer the following questions: 1.
What are the structures of the anatomy of the colon and rectum, and what is the role of the large intestine in storing and desiccating the residues of a meal?
2.
What are the motility patterns of the colon that provide for its storage function, and what reflexes signal to the colon from more proximal portions of the GI tract?
3.
What is the role of intestinal microorganisms in metabolism and host defense?
4.
What are the mechanisms that provide for defecation, and how it can be delayed until convenient?
Overview of the Large Intestine
The most distal segment of the gastrointestinal (GI) tract, the large intestine, comprises the cecum; ascending, transverse, and descending portions of the colon; rectum; and anus (